1. Field of Invention
This invention relates to wireless communications systems. Specifically, the present invention relates to receivers for demodulating quick paging channels in communications systems employing more than one paging channel to facilitate offline processing.
2. Description of the Related Art
Wireless communications systems are employed in a variety of demanding applications ranging from search and rescue to Internet applications. Such applications require reliable, cost-effective, and space-efficient communications systems with accompanying wireless phones having maximum battery life and associated standby time.
Cellular telecommunications systems, such as Code Division Multiple access (CDMA) communications systems, are often characterized by a plurality of mobile stations (e.g. cellular telephones, mobile units, wireless telephones, or mobile phones) in communication with one or more Base Station Transceiver Subsystems (BTS""s). Signals transmitted by the mobile stations are received by a BTS and often relayed to a Mobile Switching Center (MSC) having a Base Station Controller (BSC). The MSC, in turn, routes the signal to a Public Switched Telephone Network (PSTN) or to another wireless phone. Similarly, a signal may be transmitted from the Public Switched Telephone Network to a wireless phone via a base station or BTS and an MSC.
Wireless communications networks often employ various channels, such as paging channels and traffic channels, as disclosed in the IS-95 cellular telephone standard, to facilitate communications between a wireless phone and a BTS. Paging messages are transmitted over a paging channel by a BTS to an associated wireless phone to indicate an incoming call. When a wireless phone detects a paging message, a sequence of service negotiation messages is transmitted between the wireless phone and an associated BTS to establish a traffic channel. A traffic channel typically supports voice and data traffic.
Conventionally, a wireless telephone continuously monitors the paging channel for pages indicative of incoming calls. The receiver of the wireless phone remains on while signal processing circuitry within the wireless phone demodulates the paging channel to determine if a page was sent. Unfortunately, the receiver draws excess power, which significantly limits phone battery life.
Systems for minimizing wireless phone power consumption are often employed in the wireless phone and/or accompanying network to extend phone battery life, i.e., standby time. To improve standby time, some newer wireless phones operate in slotted mode. In slotted mode, the receiver of the wireless phone is periodically activated in accordance with predetermined paging slots established in accordance with the IS-95 telecommunications standard. An associated BTS transmits pages during the paging slots. Wireless phone standby time is extended by periodically powering-up the receiver and demodulating the paging channel rather than continuously demodulating the full paging channel as done previously.
Unfortunately, paging channel messages are often long and require extensive processing, which increases phone power consumption and reduces battery life and associated standby time. Furthermore, the design of such systems and the associated paging channels necessitates redundant processing of the lengthy paging channel messages to detect incoming calls. This further reduces phone battery life.
Further increases in phone standby time are achieved via a relatively new addition to the IS-95 telecommunications standard known as offline processing. In a wireless communications network employing offline processing, a pair of Quick Paging Channel (QPCH) symbols is periodically transmitted to the wireless phone. The quick paging channel symbols, i.e., quick pages, indicate the presence or absence of an incoming call to be established on a forthcoming traffic channel (F-CCCH). The QPCH symbols arrive in pairs at 9600 bits per second (bps) or 4800 bps. The time slots at which the QPCH symbols are transmitted from an associated BTS are known by the wireless phone, which periodically powers-up the receiver at corresponding time slots.
In a wireless phone employing offline processing, the wireless phone receiver powers-up, samples the QPCH, then immediately powers-down the receiver and processes the QPCH sample offline (when the receiver is off). Subsequent analysis of the QPCH sample or samples indicates whether the wireless phone should power-up the receiver and demodulate the paging channel to receive an incoming page associated with an incoming call. Use of the QCPH helps minimize receiver activation time and the instances of complete paging channel demodulation, enabling a reduction in wireless phone power consumption and an associated extension in phone battery life. Unfortunately, existing systems and methods for demodulating the QPCH and deciding whether or not to process the subsequent full paging channel based on the QPCH are undesirably large, expensive, consume excess power, and are generally inefficient. Furthermore, existing systems often fail to effectively employ the first symbol or both symbols of the QPCH as needed to effectively determine whether to process the forthcoming full paging channel.
Hence, a need exists in the art for an efficient and cost effective system and method for receiving and processing quick paging channel symbols to determine whether or not to process the forthcoming full paging channel. There exists a further need for an efficient system and method that selectively employs either one or both symbols of each quick paging channel slot, in accordance with the existing signal environment, to most efficiently and reliably detect the presence of an incoming page via minimal requisite hardware.
The need in the art is addressed by the efficient system for determining if a primary paging channel should be received and processed of the present invention. In the illustrative embodiment, the inventive system is adapted for use with a wireless communications device in a wireless communications system employing quick paging channel. The system includes a first mechanism for receiving an electromagnetic signal having pilot signal and quick paging signal components. A second mechanism ascertains whether a second symbol of the quick paging channel signal should be immediately analyzed based on a first quality parameter and a first decision metric associated with a first symbol of the quick paging signal and provides a first indication in response thereto. The first decision metric is representative of a value of the first symbol. A third mechanism determines, via the second symbol, whether the primary paging channel should be immediately processed based on a second quality parameter and a second decision metric associated with the second symbol. The third mechanism provides a second indication in response thereto when the first indication indicates that the second symbol should be immediately analyzed.
In a specific embodiment, the first quality parameter and the second quality parameter are based on a portion of the pilot signal associated with the first symbol and the second symbol, respectively. The first and second quality parameters are normalized pilot energies that are indicative of a quality of a signal environment in which the electromagnetic signal is propagating. The first decision metric is determined in accordance with the following metric (D1):       D    1    =            Q      ⁢              xe2x80x83            ⁢              P        1                    E              pilot        ⁢                  xe2x80x83                ⁢        1            
where D1 is the first decision metric; QP1 is the dot product, cross product, or a combination thereof (depending on the mode of the transmission) of the first symbol with an estimate of the pilot signal associated with the first symbol; and Epilot1 is an energy of the pilot signal associated with the first symbol.
The second decision metric is the demodulation symbol (D) defined in accordance with one of the following equation:       D    =                            Q          ⁢                      xe2x80x83                    ⁢                      P            1                          +                  Q          ⁢                      xe2x80x83                    ⁢                      P            2                                                E                      pilot            ⁢                          xe2x80x83                        ⁢            1                          +                  E                      pilot            ⁢                          xe2x80x83                        ⁢            2                                ,
where QP2 is the dot product, cross product, or a combination thereof (depending on the mode of the mobile station) of the second symbol with an estimate of the pilot signal associated with the second symbol, and Epilot2 is an energy of the second portion of the pilot signal.
The novel design of the present invention is facilitated by the first mechanism and the second mechanism, which strategically process the first quick paging channel symbol and/or the second paging channel signal as needed. This avoids sometimes unnecessary processing of the second quick paging channel symbol, yet provides for a maximum probability of successful detection of a forthcoming primary paging channel and reduces or eliminates instances of redundant processing of the primary paging channel.